It is readily apparent that a large number of telephone calls, both private and business, are wasted due to the unavailability of the called subscriber (where the term “subscriber” is taken here to mean a telephone user). For example, the called user may be absent from his normally used telephone, or he may be engaged in another conversation on the called telephone. It will also be apparent that a call relating to some relatively unimportant matter may lead to the interruption of an important meeting or the like.
A simple solution to this problem is to provide a human messaging service to take down a message and forward it to the called user, e.g. using an electronic or paper memo. The telecommunications industry has also implemented a number of solutions to deal with this problem. For example, a “call waiting” service has been introduced where, when a called user is engaged in an existing call, the new calling party is placed on hold and the called party is advised of the new incoming call by a tone or operator announcement. Another solution is the use of electronic telephone receptionists which intercept incoming calls, asking for the caller's name. The name is then relayed to the called party who can choose whether or not to take the call. Yet another solution is “call diversion”, where a telephone user may, for example, cause incoming calls to be diverted from his fixed line phone to his mobile phone during an absence from the office.
A disadvantage associated with many solutions is that even a failed call involves the connection of the calling party to some telephone network node, e.g. an Intelligent Network (IN) node which diverts calls and/or plays operator announcements. This will typically incur a charge against the called and/or calling party's account and, often more importantly, will consume time on the part of the calling party and the called party especially if the called party needs to return the call, only to discover that the original calling party is now unavailable on the called telephone number. Establishing a call for only a very short duration may additionally be uneconomic for telephone network operators, as the cost charged for the call may not cover the (notional) set-up cost.